The invention relates to a device for recording information on or reading information from a rotating information disc, in particular an optical disc, comprising a turntable which is rotatable about an axis of rotation and which has a supporting surface for the information disc, and a clamping device for clamping the information disc on the turntable. The clamping device comprises a disc-pressure means, a support for the disc-pressure means, which support is movable between an operating position and a rest position, and a permanent-magnet system comprising a first axially magnetized annular magnet and a second axially magnetized magnet which cooperates with said first magnet. On of the magnets is secured to the support and the other is secured to the disc-pressure means; the magnet system presses the disc-pressure means magnetically against the information disc on the turntable in the operating position of the support, in which position the disc-pressure means is freely rotatable relative to the support. As the support moves from its operating position to its rest position, it cooperates with the disc-pressure means to move the disc-pressure means away from the information disc and thus release the information disc, the support carrying the disc-pressure means in its rest position.
Such a device is known from Netherlands Patent Application No. 8202163, to which U.S. Pat. No. 4,768,185 corresponds, herewith incorporated by reference. The known device is intended for use in a videodisc player having a cover which when in its closed position can be swung open to place a video disc on or remove it from the turntable. The cover then functions as a support for the disc-pressure means and is provided with one of the magnets of the permanent-magnet system. The magnet system comprises two annular permanent magnets which are axially disposed one about the other and concentrically around a central portion of the disc-pressure means. The magnets are axially magnetized and arranged one above the other in such a way that their pole faces of like polarity face each other, an axial air gap being formed between the facing pole faces. Between the support and the disc-pressure means a magnetic force is exerted, pressing the disc-pressure means against a cover portion in the rest position of the support. In the operating position of the support the cover has moved so far that the disc-pressure means, which is clear of the cover, presses against a video disc on the turntable, the axial air gap between the magnets then being smaller than in the rest position of the support.
The clamping device of the known video-disc player has the disadvantage that the superposed repelling permanent magnets occupy an unstable radial position relative to one another. As a result of this, even small radial displacements of the magnets relative to one another, for example caused by vibrations of the optical-disc player, may give rise to radially directed shear forces between the support and the disc-pressure means. In the operating position of the support this may lead to structural parts, such as the bearing means of the turntable, being loaded additionally and it may give rise to the tracking movements of the scanning element of the player being impaired. A further consequence of the unstable position of the magnets relative to one another is that the disc-pressure means must have a central bore in which a free end portion of the drive spindle of the turntable is engageable during the movement of the support from its rest position to its operating position to pre-center the disc-pressure means relative to the turntable.